Our version of ppc bitops produces the following compiler warnings:

/ptx/work/octopus/WORK_1/sha/u-boot/barebox/arch/ppc/include/asm/bitops.h:
In function 'ext2_find_next_zero_bit':
/ptx/work/octopus/WORK_1/sha/u-boot/barebox/arch/ppc/include/asm/bitops.h:294:
warning: '__swab32p' is static but used in inline function 'ext2_find_next_zero_bit' which is not static

Looking at the kernel ext2_find_next_zero_bit is defined as
generic_find_next_zero_le_bit which is in generic kernel code.

We currently do not need this, so do the very same define to silence the
compiler. If somebody ever needs this function, the resulting error
should give him a hint what to do.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>