riscv: Fix unused variable warning when BUILTIN_DTB is set

commit ef69d25 ("riscv: Move early dtb mapping into the fixmap
region") wrongly moved the #ifndef CONFIG_BUILTIN_DTB surrounding the pa
variable definition in create_fdt_early_page_table(), so move it back to
its right place to quiet the following warning:

../arch/riscv/mm/init.c: In function ‘create_fdt_early_page_table’:
../arch/riscv/mm/init.c:925:12: warning: unused variable ‘pa’ [-Wunused-variable]
  925 |  uintptr_t pa = dtb_pa & ~(PMD_SIZE - 1);

Fixes: ef69d25 ("riscv: Move early dtb mapping into the fixmap region")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230519131311.391960-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Alexandre Ghiti

arch/riscv/mm/init.c

@@ -922,9 +922,9 @@ static void __init create_kernel_page_table(pgd_t *pgdir, bool early)
 static void __init create_fdt_early_page_table(uintptr_t fix_fdt_va,
 					       uintptr_t dtb_pa)
 {
+#ifndef CONFIG_BUILTIN_DTB
 	uintptr_t pa = dtb_pa & ~(PMD_SIZE - 1);
 
-#ifndef CONFIG_BUILTIN_DTB
 	/* Make sure the fdt fixmap address is always aligned on PMD size */
 	BUILD_BUG_ON(FIX_FDT % (PMD_SIZE / PAGE_SIZE));