Use longer jump in riscv/crt0.S

Simple `jal` fails to link when seL4 is built with user API
functions defined as public.

Signed-off-by: Marcin Witkowski <mwitkowski@antmicro.com>

(cherry picked from commit 6e1f8136e0627e1a349a6dc08879c2999fb9957d)
Change-Id: I3dc46264f10e27a9e841d11b99a5002b8ca927ca

crt/arch/riscv/crt0.S

diff --git a/crt/arch/riscv/crt0.S b/crt/arch/riscv/crt0.S
index 8bbef72..c227148 100644
--- a/crt/arch/riscv/crt0.S
+++ b/crt/arch/riscv/crt0.S
@@ -38,10 +38,10 @@
 .option pop
 
 	li s0, 0
-	li ra, 0
 
 	addi  a0, sp, 0
-	jal  ra, __sel4_start_c
+	la x5, __sel4_start_c
+	jalr ra, x5, 0
 
 	/* should not return */
 1: