docs: arm64: Fix ICC_SRE_EL2 register typo in booting.rst

Fix trivial ICC_SRE_EL2 register spelling typo in booting.rst.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Will Deacon <will@kernel.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250610120935.852034-1-lpieralisi@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>