package/musl: bump to version 1.2.1

package/musl: bump to version 1.2.1

The license file has seen a few changes, but the overall license
remains MIT. Details of the changes:

--- output/build/musl-1.2.0/COPYRIGHT	2020-02-21 01:37:02.000000000 +0100
+++ output/build/musl-1.2.1/COPYRIGHT	2020-08-04 06:21:09.000000000 +0200
@@ -127,10 +127,13 @@
 and labelled as such in comments in the individual source files. All
 have been licensed under extremely permissive terms.

-The ARM memcpy code (src/string/arm/memcpy_el.S) is Copyright © 2008
+The ARM memcpy code (src/string/arm/memcpy.S) is Copyright © 2008
 The Android Open Source Project and is licensed under a two-clause BSD
 license. It was taken from Bionic libc, used on Android.

+The AArch64 memcpy and memset code (src/string/aarch64/*) are
+Copyright © 1999-2019, Arm Limited.
+
 The implementation of DES for crypt (src/crypt/crypt_des.c) is
 Copyright © 1994 David Burren. It is licensed under a BSD license.

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>