parisc: Fix wrong comment for shr macro

The comment that the source and target register can not be the same is
wrong. Instead on PA2.0 usage of extru can clobber upper 32-bits.
This patch fixes the comment.
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/assembly.h

@@ -143,7 +143,7 @@
 	depd,z	\r, 63-(\sa), 64-(\sa), \t
 	.endm
 
-	/* Shift Right - note the r and t can NOT be the same! */
+	/* Shift Right for 32-bit. Clobbers upper 32-bit on PA2.0. */
 	.macro shr r, sa, t
 	extru \r, 31-(\sa), 32-(\sa), \t
 	.endm