crypto: hisilicon/hpre - fix memory leak in hpre_curve25519_src_init()

hpre_curve25519_src_init() allocates memory for 'ptr' before calling
memcmp(). If memcmp() returns 0, the function will return '-EINVAL'
without freeing memory.

Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>