linux/bitmap.h: fix type of nbits in bitmap_shift_right()

Most other bitmap API, including the OOL version __bitmap_shift_right,
take unsigned nbits.  This was accidentally left out from 2fbad299.

Link: http://lkml.kernel.org/r/20180818131623.8755-5-linux@rasmusvillemoes.dk


Fixes: 2fbad299 ("lib: bitmap: change bitmap_shift_right to take unsigned parameters")
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: Yury Norov <ynorov@caviumnetworks.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>