mmu_pte_psize is only used in the tlb_64e.c, define it static.

Fixes: 25d21ad6 ("powerpc: Add TLB management code for 64-bit Book3E")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408011256.1O99IB0s-lkp@intel.com/Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/beb30d280eaa5d857c38a0834b147dffd6b28aa9.1724157750.git.christophe.leroy@csgroup.eu