create_inode: fix gcc -Wall warnings #78

Job	Run time
Build and test with ASAN enabled	1m 42s
Build and test with clang	1m 13s
Cross-compile for Android (aarch64)	36s
Build and test with gcc	1m 8s
Build and test with gcc -m32	1m 14s
Cross-compile for Android (armv7a)	34s
Build and test on macOS	2m 1s
Cross-compile for Android (i686)	30s
Cross-compile for Android (x86_64)	33s
Build and test with UBSAN enabled	1m 16s
Build mke2fs on Windows with mingw32	2m 20s
Build mke2fs on Windows with mingw64	2m 10s
	15m 17s

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