x86/Kconfig: fix the spelling of 'becoming' in X86_KERNEL_IBT config

There is only one m in becoming.

Signed-off-by: Nur Hussein <hussein@unixcat.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220417192454.10247-1-hussein@unixcat.org