auxdisplay: img-ascii-lcd: kconfig: Remove MIPS_SEAD3 reference

Commit 3f5f0a44 ("MIPS: generic: Convert SEAD-3 to a generic board")
removed the MIPS_SEAD3 symbol and moved the setting of IMG_ASCII_LCD to
the board-sead-3.config defconfig file, but IMG_ASCII_LCD still
references the removed MIPS_SEAD3 symbol.

Remove the reference.

Discovered with the
https://github.com/ulfalizer/Kconfiglib/blob/master/examples/list_undefined.py
script.
Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

drivers/auxdisplay/Kconfig

@@ -137,7 +137,7 @@ config CFAG12864B_RATE
 config IMG_ASCII_LCD
 	tristate "Imagination Technologies ASCII LCD Display"
 	depends on HAS_IOMEM
-	default y if MIPS_MALTA || MIPS_SEAD3
+	default y if MIPS_MALTA
 	select SYSCON
 	help
 	  Enable this to support the simple ASCII LCD displays found on