arm64: Fix the documented event stream frequency

arm64: Fix the documented event stream frequency

It should be 10KHz, matching the ARCH_TIMER_EVT_STREAM_PERIOD_US of
100us.

Note that this is only a documentation bug.

Fixes: cd96af6ce852 ("arm64: docs: describe ELF hwcaps")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20210505132845.23698-1-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>