treewide: fix typos of SPDX-License-Identifier

Prior to the adoption of SPDX, it was difficult for tools to determine
the correct license due to incomplete or badly formatted license text.
The SPDX solves this issue, assuming people can correctly spell
"SPDX-License-Identifier" although this assumption is broken in some
places.

Since scripts/spdxcheck.py parses only lines that exactly matches to
the correct tag, it cannot (should not) detect this kind of error.

If the correct tag is missing, scripts/checkpatch.pl warns like this:

 WARNING: Missing or malformed SPDX-License-Identifier tag in line *

So, people should notice it before the patch submission, but in reality
broken tags sometimes slip in. The checkpatch warning is not useful for
checking the committed files globally since large number of files still
have no SPDX tag.

Also, I am not sure about the legal effect when the SPDX tag is broken.

Anyway, these typos are absolutely worth fixing. It is pretty easy to
find suspicious lines by grep.

  $ git grep --not -e SPDX-License-Identifier --and -e SPDX- -- \
    :^LICENSES :^scripts/spdxcheck.py :^*/license-rules.rst
  arch/arm/kernel/bugs.c:// SPDX-Identifier: GPL-2.0
  drivers/phy/st/phy-stm32-usbphyc.c:// SPDX-Licence-Identifier: GPL-2.0
  drivers/pinctrl/sh-pfc/pfc-r8a77980.c:// SPDX-Lincense-Identifier: GPL 2.0
  lib/test_stackinit.c:// SPDX-Licenses: GPLv2
  sound/soc/codecs/max9759.c:// SPDX-Licence-Identifier: GPL-2.0
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm/kernel/bugs.c

-// SPDX-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0
 #include <linux/init.h>
 #include <asm/bugs.h>
 #include <asm/proc-fns.h>

drivers/phy/st/phy-stm32-usbphyc.c

-// SPDX-Licence-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0
 /*
  * STMicroelectronics STM32 USB PHY Controller driver
  *

drivers/pinctrl/sh-pfc/pfc-r8a77980.c

-// SPDX-Lincense-Identifier: GPL 2.0
+// SPDX-License-Identifier: GPL-2.0
 /*
  * R8A77980 processor support - PFC hardware block.
  *

lib/test_stackinit.c

-// SPDX-Licenses: GPLv2
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Test cases for compiler-based stack variable zeroing via future
  * compiler flags or CONFIG_GCC_PLUGIN_STRUCTLEAK*.

sound/soc/codecs/max9759.c

-// SPDX-Licence-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0
 /*
  * MAX9759 Amplifier Driver
  *