crypto: lib/mpi - Use swap() in mpi_powm()

Use existing swap() function rather than duplicating its implementation.

./lib/crypto/mpi/mpi-pow.c:211:11-12: WARNING opportunity for swap().
./lib/crypto/mpi/mpi-pow.c:239:12-13: WARNING opportunity for swap().
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9327Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/crypto/mpi/mpi-pow.c

@@ -176,7 +176,6 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 
 		for (;;) {
 			while (c) {
-				mpi_ptr_t tp;
 				mpi_size_t xsize;
 
 				/*if (mpihelp_mul_n(xp, rp, rp, rsize) < 0) goto enomem */
@@ -207,9 +206,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 					xsize = msize;
 				}
 
-				tp = rp;
-				rp = xp;
-				xp = tp;
+				swap(rp, xp);
 				rsize = xsize;
 
 				if ((mpi_limb_signed_t) e < 0) {
@@ -235,9 +232,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 						xsize = msize;
 					}
 
-					tp = rp;
-					rp = xp;
-					xp = tp;
+					swap(rp, xp);
 					rsize = xsize;
 				}
 				e <<= 1;