Fix the following -Werror warning from clang 10.0.0:

sys/arm64/arm64/identcpu.c:1170:5: error: misleading indentation; statement is not part of the previous 'if' [-Werror,-Wmisleading-indentation]

break;
^

sys/arm64/arm64/identcpu.c:1168:4: note: previous statement is here

if (fv[j].desc[0] != '\0')
^

The break should be after the if statement, indented one level less.

MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D23871