configure: Remove -Winline

I'm getting the following errors when compiling with --enable-werror:

 kboot-parser.c: In function 'kboot_process_pair':
 ./parser-conf.h:50:21: error: inlining failed in call to 'conf_get_pair_equal':
 call is unlikely and code size would grow [-Werror=inline]
 kboot-parser.c:65:7: error: called from here [-Werror=inline]

Since this is a header function, the inline isn't there for optimisation
reasons; the warning is just informing us of a code optimisation
decision. Drop -Winline to allow -Werror builds.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>