lib/test_find_bit.c: rename to find_bit_benchmark.c

lib/test_find_bit.c: rename to find_bit_benchmark.c

As suggested in review comments, rename test_find_bit.c to
find_bit_benchmark.c.

Link: http://lkml.kernel.org/r/20171124143040.a44jvhmnaiyedg2i@yury-thinkpad
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Clement Courbet <courbet@google.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>