Fix initramfs hook for merged /usr/lib and /lib

Under a merged /lib -> /usr/lib which renders /lib as a symlink,
find /lib -type f -name libgcc_s.so.1 will not return a result as
find will not traverse the symlink. Modifying it to `find /lib/ -type
f -name libgcc_s.so.1` should work for both symlinked and non-symlinked
/lib directories.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Kemp <matt@mattikus.com>
Closes #5834