kbuild: clean up asm-offsets.h creation
kbuild: clean up asm-offsets.h creation

- Move mkdir out of cmd_offsets
- Add input file to sed command instead of using cat

Signed-off-by: Brian Gerst <b2407f8e4103fa23f975bfdebd5f2cf99075709e@didntduck.org>
Signed-off-by: Sam Ravnborg <f16bed56189e249fe4ca8ed10a1ecae60e8ceac0@ravnborg.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs