efi: efibc: change kmalloc(size * count, ...) to kmalloc_array()

Open coded arithmetic in allocator arguments is discouraged. Helper
functions like kcalloc or, in this case, kmalloc_array are preferred.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments



Signed-off-by: Ethan Carter Edwards <ethan@ethancedwards.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>